The present invention relates to a press or similar machine tool having a reciprocating tool carrier. The tool carrier is moved by means of two identical buckling toggle-lever systems. The toggle-lever systems are driven by a drive means supported on the tool carrier and located between the toggle-lever systems.
German Offenlegungsschrift No. 2,755,962, herein incorporated by reference, discloses a press of this type, in which the drive is effected by a crank drive located in the closed toggle-lever system.
Said prior art system, which combines the advantages of the toggle-lever presses with that of the crank drive in an almost ideal manner, is particularly suitable for automatic operation at high stroke frequencies. The asymmetrical arrangement of the press in the above cited publication, particularly in conjunction with a high rate of operation, causes the tool carrier especially the guide on the ram side to undergo high stress which can, depending on the particular usage, lead to rapid wear and tear.
The proposal to use a crank drive exclusively as the drive for toggle-lever presses is considered to be very restrictive, since this system is unsuited for universal application.
This is particularly true for presses the operation of which are subject to strict safety regulations, specifically with a view to precise braking and avoidance of over-run.
A crank device can, in general, meet these conditions with adequate safety but not with complete safety, in spite of the relatively low energy build-up in the drive system of such crank drive mechanisms.
Regardless of the above, the drive proposed in the above German Patent Publication offers several significant advantages. In contrast to conventional toggle-lever drives, the working shaft, with its eccentric power take-off, and hence the counter-force, need not be accommodated by the machine frame. Instead, the relatively light drive is located within the system. Thus, the counter-force largely acts, by virtue of the closed nature of the system, on the ram or tool carrier, whereby the machine stand or frame may be of lighter construction.